[Radiance-general] BSDF question

Thu Jul 3 00:45:52 PDT 2014

Germán and Andy,

meanwhile thank you for the answers and sorry if my questions are a little
bit confused. I am a newbie of the "lighting art" and I am studying this
concepts almost alone.
So if I understood, when I create a BSDF matrix with genBSDF I add the +f
+b options in order to obtain both transmission matrix and then dctimestep
does the rest, doesn't it?

Thanks for yours great help,
Giuseppe

2014-07-02 19:12 GMT+02:00 Andrew McNeil <amcneil at lbl.gov>:

> Giuseppe,
>
> The front/back inconsistency is mostly related to the BSDF material
> primitive. For the 3-phase method you don't have to worry about front/back
> of the fenestration. (unless you want to use a BSDF backwards, which might
> be impossible without manually editing the BSDF file).
>
> The BSDF handling has matured quite a bit since the early days of the
> three-phase method. These days dctimestep can use either front transmission
> or back transmission applying reciprocity principles for the three phase
> method.
>
> Andy
>
>
>
>
> On Wed, Jul 2, 2014 at 9:24 AM, CHI-German Molina <gmolina at hdlao.com>
> wrote:
>
>> Guiseppe,
>>
>> The three-phase method simulation method does not use the geometry of the
>> shading device to work. In fact, one advantage of it is that only the
>> BSDF.xml file is needed. If you check Andy's Three-phase method tutorial,
>> you will see that the calculation of the V and D matrices do not require
>> neither the geometry of the shading device nor the BSDF of it (thus making
>> it very easy to try multiple fenestration systems).
>>
>> Adding Geometry information to the BSDF file is useful for using pkgBSDF;
>> not really for the 3phase method. When rays have to go through the
>> fenestration system (i.e. rendering a room with venetian blinds, or  when
>> calculating the third matrix of the 5 phase method) a combination of two
>> illums that "wrap" the geometry and the geometry itself seems to be more
>> efficient. My understanding (I might be completely wrong) is that the
>> illums are used to transfer the diffuse (indirect??) radiation; and the
>> geometry is used for transfering direct radiation, casting shadows.
>>
>> My answer to the first question:
>>
>> *1.  in the equation i=VTDs the T matrix has to contain the window
>> geometry or take knowledge of these from the other two matrix(V,D)? *
>>
>> Nope. After the V and D matrices are calculated, the simulation is
>> performed by simply multiplying matrices... no geometry.
>>
>>
>> The second question is something that confuses me... it would be good to
>> have clarification here.
>>
>> Hope this helps!
>>
>> Germán
>>
>>
>> 2014-07-02 11:54 GMT-04:00 Giuseppe De Michele <giudm.87 at gmail.com>:
>>
>>> Dear all,
>>>
>>> I am working with the 3 phase method (only from a few weeks) and I am
>>> trying to understand the BSDF file format and how the 3 phase method read
>>> it.
>>>
>>>  I have noticed that if I use the bsdf created with the command:
>>> genBSDF -n 4 +f +b -geom meter material.rad blinds.rad > blinds.xml
>>> the .xml file contain same geometrical dimension (height, width). In
>>> fact if I use the command:
>>> pkgBSDF -s blinds.xml > blinds_pkg.rad
>>> the output file contain the original geometry.
>>>
>>> Instead if I use the BSDF created or contained  in the database of
>>> WINDOW 7 these file do not contain a geometry.
>>> With pkgBSDF I got an error.
>>>
>>> My questions are:
>>> 1.  in the equation i=VTDs the T matrix has to contain the window
>>> geometry or take knowledge of these from the other two matrix(V,D)?
>>> 2.  I have understood that 3 phase method uses only the front
>>> transmission data [A. McNeil, Three-Phase Method tutorial]  but in
>>>  an other discussion [
>>> http://www.radiance-online.org/pipermail/radiance-general/2012-October/008969.html
>>> ]  I have discovered that WINDOW and genBSDF use an opposite meaning of
>>> front and back, so the front transmission regards radiance or window
>>> meaning?And what part of the T matrix I have to use in the 3 phase method
>>> for the respective cases (WINDOW or genBSDF)?
>>>
>>> Kind regards,
>>> *Giuseppe*
>>>
>>> _______________________________________________
>>> Radiance-general mailing list
>>> Radiance-general at radiance-online.org
>>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>>
>>>
>>
>>
>> --
>> *Germán Molina L.*
>> Ingeniero Trainee
>> Hunter Douglas Chile S.A.
>> Celular +569 89224445
>>
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-- 
*Giuseppe De Michele*
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